1. Field of the Invention
This invention relates to a base sheet for a roofing assembly wherein the base sheet is perforated by a plurality of a cluster of apertures for allowing the flow of an adhesive therethrough for bonding the base sheet to an underlying substrate.
2. Reported Developments
A roofing assembly typically comprises: a substrate or deck having an interior surface facing the internal area of the building, and an exterior surface; an insulating layer or sheet covering the exterior surface; a base sheet covering the insulating layer and rendering the underlying assembly impervious to the elements but allowing for the breathing out of moisture which might be trapped in the underlying assembly; a membrane and a surface or finishing layer on top of the membrane completing the roofing assembly.
The substrate or deck can be made of gypsum, cement, wood, metals or a synthetic material sufficient to provide structural integrity to the roofing assembly.
The insulating layer is constructed of a rigid or semi-rigid material to reduce thermal fluctuation and includes such materials as Perlite, polystyrene, polyurethane, isocyanurate, fiber boards and foam glass.
The base sheet is composed of an organic or inorganic material, saturated or coated with oxidized or unoxidized asphalt, polymer modified asphalt or coal tar. The top and under surfaces of the base sheet are coated with an asphaltic material in which granules or particulates are embedded to allow ventilation therethrough. The base sheet is contacted with a release agent, such as sand, talc or a soap to prevent sticking between the layers when the layers are formed into rolls for shipping.
The base sheet is perforated in order to provide a plurality of holes for allowing penetration of a flowable bonding agent so that the base sheet may be bonded to the underlying substrate. Such bonding agents include asphalts and coal tar pitch having softening points of from about 100.degree. to about 500.degree. F. The bonding material may contain a mineral stabilizer, such as that derived from limestone, stone powder, sand or other fine mineral particles. At the point of application, the bonding agent is heated to a flowable condition. The heated bonding agent flows through the perforations and bond the base sheet to the substrate at the point of perforations in the marginal areas thereof, while the unbounded areas between the perforations allow for venting of vapors which may build up due to changes in temperature and humidity. The marginal areas of perforations where the bonding agent secures the base sheet to the underlying substrate insures against wind uplift, i.e., to prevent the separation of the base sheet from the underlying surface.
A persistent problem associated with roofing assembly, especially during the process of construction thereof, is wind uplift which results in the separation of the base sheet from the underlying substrate. In areas of high wind velocity and during construction under inclement weather condition it has been difficult to achieve the wind uplift resistance without using cost prohibitive construction techniques. Convenient and inexpensive methods were taught in the prior art for example, as disclosed in U.S. Pat. Nos. 3,135,069 and 4,567,079 in which the base sheet carries a plurality of uniformly sized and spaced apertures or perforations which allow flowthrough of a bonding agent to secure the base sheet to the underlying substrate.
While this method is cost and time saving in that it eliminates the need for securing devices at critical intervals, it has not been found effective in environments subject to relatively high wind velocities since the base sheets containing a plurality of uniformly spaced perforations currently available do not provide sufficient adhesive force when a bonding agent is flown therethrough and sheet integrity to resist strong wind uplift forces. In the case of a conventionally perforated base sheet, merely widening the circular perforations or increasing their number is not a viable solution since these approaches decrease the strength of the base sheet.
Accordingly, it is an object of the present invention to provide an improved base sheet having uniquely positioned apertures therein for attachment of the base sheet to an underlying substrate by the use of a flowable bonding substance.
It is a main object of the present invention to provide a roofing assembly comprising a base sheet having uniquely positioned apertures therein which, as part of the roofing assembly, has superior resistance to wind uplift forces.
These and other objects and advantages will be more apparent from the description that follows.